Two Dynamic System Settings control the use of lightweight lists by the Obj-Browse method. There is a setting each for the Pega 7 Platform and application rules:
clipboard/lightWeightList/enableForCorePRPCRules – this is set to true by default.
clipboard/lightWeightList/enableForCustomerRules – this is set to false by default.
When true, these Dynamic System Settings override the Use Lightweight List check box setting on the Activity rule form.